[PATCH bpf-next 13/18] selftests/bpf: Add verifier tests for stack argument validation

Yonghong Song
2026-04-24T17:17:16Z

Add inline-asm based verifier tests that exercise stack argument
validation logic directly.

Positive tests:
- subprog call with 6 arg's
- Two sequential calls to different subprogs (6-arg and 7-arg)
- Share a r11 store for both branches

Negative tests — verifier rejection:
- Read from uninitialized incoming stack arg slot
- Gap in outgoing slots: only r11-16 written, r11-8 missing
- Write at r11-80, exceeding max 7 stack args
- Missing store on one branch with a shared store
- First call has proper stack arguments and the second
call intends to inherit stack arguments but not working
- r11 load ordering issue

Negative tests — pointer/ref tracking:
- Pruning type mismatch: one branch stores PTR_TO_STACK, the
other stores a scalar, callee dereferences — must not prune
- Release invalidation: bpf_sk_release invalidates a socket
pointer stored in a stack arg slot
- Packet pointer invalidation: bpf_skb_pull_data invalidates
a packet pointer stored in a stack arg slot
- Null propagation: PTR_TO_MAP_VALUE_OR_NULL stored in stack
arg slot, null branch attempts dereference via callee

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
.../selftests/bpf/prog_tests/verifier.c | 2 +
.../selftests/bpf/progs/verifier_stack_arg.c | 456 ++++++++++++++++++
2 files changed, 458 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/verifier_stack_arg.c

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index a96b25ebff23..aef21cf2987b 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -91,6 +91,7 @@
#include "verifier_sockmap_mutate.skel.h"
#include "verifier_spill_fill.skel.h"
#include "verifier_spin_lock.skel.h"
+#include "verifier_stack_arg.skel.h"
#include "verifier_stack_ptr.skel.h"
#include "verifier_store_release.skel.h"
#include "verifier_subprog_precision.skel.h"
@@ -238,6 +239,7 @@ void test_verifier_sock_addr(void) { RUN(verifier_sock_addr); }
void test_verifier_sockmap_mutate(void) { RUN(verifier_sockmap_mutate); }
void test_verifier_spill_fill(void) { RUN(verifier_spill_fill); }
void test_verifier_spin_lock(void) { RUN(verifier_spin_lock); }
+void test_verifier_stack_arg(void) { RUN(verifier_stack_arg); }
void test_verifier_stack_ptr(void) { RUN(verifier_stack_ptr); }
void test_verifier_store_release(void) { RUN(verifier_store_release); }
void test_verifier_subprog_precision(void) { RUN(verifier_subprog_precision); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
new file mode 100644
index 000000000000..6b596ad63774
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
@@ -0,0 +1,456 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(max_entries, 1);
+ __type(key, long long);
+ __type(value, long long);
+} map_hash_8b SEC(".maps");
+
+#if defined(__TARGET_ARCH_x86) && defined(__BPF_FEATURE_STACK_ARGUMENT)
+
+__noinline __used
+static int subprog_6args(int a, int b, int c, int d, int e, int f)
+{
+ return a + b + c + d + e + f;
+}
+
+__noinline __used
+static int subprog_7args(int a, int b, int c, int d, int e, int f, int g)
+{
+ return a + b + c + d + e + f + g;
+}
+
+__noinline __used
+static long subprog_deref_arg6(long a, long b, long c, long d, long e, long *f)
+{
+ return *f;
+}
+
+SEC("tc")
+__description("stack_arg: subprog with 6 args")
+__success
+__naked void stack_arg_6args(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u64 *)(r11 - 8) = 6;"
+ "call subprog_6args;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: two subprogs with >5 args")
+__success
+__naked void stack_arg_two_subprogs(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u64 *)(r11 - 8) = 10;"
+ "call subprog_6args;"
+ "r6 = r0;"
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u64 *)(r11 - 16) = 30;"
+ "*(u64 *)(r11 - 8) = 20;"
+ "call subprog_7args;"
+ "r0 += r6;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: read from uninitialized stack arg slot")
+__failure
+__msg("invalid read from stack arg off 8 depth 0")
+__naked void stack_arg_read_uninitialized(void)
+{
+ asm volatile (
+ "r0 = *(u64 *)(r11 + 8);"
+ "r0 = 0;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: gap at offset -8, only wrote -16")
+__failure
+__msg("stack *(R11-8) not properly initialized")
+__naked void stack_arg_gap_at_minus8(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u64 *)(r11 - 16) = 30;"
+ "call subprog_7args;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: pruning with different stack arg types")
+__failure
+__flag(BPF_F_TEST_STATE_FREQ)
+__msg("invalid mem access 'scalar'")
+__naked void stack_arg_pruning_type_mismatch(void)
+{
+ asm volatile (
+ "call %[bpf_get_prandom_u32];"
+ "r6 = r0;"
+ /* local = 0 on program stack */
+ "r7 = 0;"
+ "*(u64 *)(r10 - 8) = r7;"
+ /* Branch based on random value */
+ "if r6 s> 3 goto l0_%=;"
+ /* Path 1: store stack pointer to outgoing arg6 */
+ "r1 = r10;"
+ "r1 += -8;"
+ "*(u64 *)(r11 - 8) = r1;"
+ "goto l1_%=;"
+ "l0_%=:"
+ /* Path 2: store scalar to outgoing arg6 */
+ "*(u64 *)(r11 - 8) = 42;"
+ "l1_%=:"
+ /* Call subprog that dereferences arg6 */
+ "r1 = r6;"
+ "r2 = 0;"
+ "r3 = 0;"
+ "r4 = 0;"
+ "r5 = 0;"
+ "call subprog_deref_arg6;"
+ "exit;"
+ :: __imm(bpf_get_prandom_u32)
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: release_reference invalidates stack arg slot")
+__failure
+__msg("invalid mem access 'scalar'")
+__naked void stack_arg_release_ref(void)
+{
+ asm volatile (
+ "r6 = r1;"
+ /* struct bpf_sock_tuple tuple = {} */
+ "r2 = 0;"
+ "*(u32 *)(r10 - 8) = r2;"
+ "*(u64 *)(r10 - 16) = r2;"
+ "*(u64 *)(r10 - 24) = r2;"
+ "*(u64 *)(r10 - 32) = r2;"
+ "*(u64 *)(r10 - 40) = r2;"
+ "*(u64 *)(r10 - 48) = r2;"
+ /* sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof(tuple), 0, 0) */
+ "r1 = r6;"
+ "r2 = r10;"
+ "r2 += -48;"
+ "r3 = %[sizeof_bpf_sock_tuple];"
+ "r4 = 0;"
+ "r5 = 0;"
+ "call %[bpf_sk_lookup_tcp];"
+ /* r0 = sk (PTR_TO_SOCK_OR_NULL) */
+ "if r0 == 0 goto l0_%=;"
+ /* Store sock ref to outgoing arg6 slot */
+ "*(u64 *)(r11 - 8) = r0;"
+ /* Release the reference — invalidates the stack arg slot */
+ "r1 = r0;"
+ "call %[bpf_sk_release];"
+ /* Call subprog that dereferences arg6 — should fail */
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call subprog_deref_arg6;"
+ "l0_%=:"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_sk_lookup_tcp),
+ __imm(bpf_sk_release),
+ __imm_const(sizeof_bpf_sock_tuple, sizeof(struct bpf_sock_tuple))
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: pkt pointer in stack arg slot invalidated after pull_data")
+__failure
+__msg("invalid mem access 'scalar'")
+__naked void stack_arg_stale_pkt_ptr(void)
+{
+ asm volatile (
+ "r6 = r1;"
+ "r7 = *(u32 *)(r6 + %[__sk_buff_data]);"
+ "r8 = *(u32 *)(r6 + %[__sk_buff_data_end]);"
+ /* check pkt has at least 1 byte */
+ "r0 = r7;"
+ "r0 += 8;"
+ "if r0 > r8 goto l0_%=;"
+ /* Store valid pkt pointer to outgoing arg6 slot */
+ "*(u64 *)(r11 - 8) = r7;"
+ /* bpf_skb_pull_data invalidates all pkt pointers */
+ "r1 = r6;"
+ "r2 = 0;"
+ "call %[bpf_skb_pull_data];"
+ /* Call subprog that dereferences arg6 — should fail */
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call subprog_deref_arg6;"
+ "l0_%=:"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_skb_pull_data),
+ __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)),
+ __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end))
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: null propagation rejects deref on null branch")
+__failure
+__msg("invalid mem access 'scalar'")
+__naked void stack_arg_null_propagation_fail(void)
+{
+ asm volatile (
+ "r1 = 0;"
+ "*(u64 *)(r10 - 8) = r1;"
+ /* r0 = bpf_map_lookup_elem(&map_hash_8b, &key) */
+ "r2 = r10;"
+ "r2 += -8;"
+ "r1 = %[map_hash_8b] ll;"
+ "call %[bpf_map_lookup_elem];"
+ /* Store PTR_TO_MAP_VALUE_OR_NULL to outgoing arg6 slot */
+ "*(u64 *)(r11 - 8) = r0;"
+ /* null check on r0 */
+ "if r0 != 0 goto l0_%=;"
+ /*
+ * On null branch, outgoing slot is SCALAR(0).
+ * Call subprog that dereferences arg6 — should fail.
+ */
+ "r1 = 0;"
+ "r2 = 0;"
+ "r3 = 0;"
+ "r4 = 0;"
+ "r5 = 0;"
+ "call subprog_deref_arg6;"
+ "l0_%=:"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_map_lookup_elem),
+ __imm_addr(map_hash_8b)
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: missing store on one branch")
+__failure
+__msg("stack *(R11-8) not properly initialized")
+__naked void stack_arg_missing_store_one_branch(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ /* Write arg7 (r11-16) before branch */
+ "*(u64 *)(r11 - 16) = 20;"
+ "call %[bpf_get_prandom_u32];"
+ "if r0 > 0 goto l0_%=;"
+ /* Path 1: write arg6 and call */
+ "*(u64 *)(r11 - 8) = 10;"
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call subprog_7args;"
+ "goto l1_%=;"
+ "l0_%=:"
+ /* Path 2: missing arg6 store, call should fail */
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call subprog_7args;"
+ "l1_%=:"
+ "r0 = 0;"
+ "exit;"
+ :: __imm(bpf_get_prandom_u32)
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: share a store for both branches")
+__success __retval(0)
+__naked void stack_arg_shared_store(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ /* Write arg7 (r11-16) before branch */
+ "*(u64 *)(r11 - 16) = 20;"
+ "call %[bpf_get_prandom_u32];"
+ "if r0 > 0 goto l0_%=;"
+ /* Path 1: write arg6 and call */
+ "*(u64 *)(r11 - 8) = 10;"
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call subprog_7args;"
+ "goto l1_%=;"
+ "l0_%=:"
+ /* Path 2: also write arg6 and call */
+ "*(u64 *)(r11 - 8) = 30;"
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call subprog_7args;"
+ "l1_%=:"
+ "r0 = 0;"
+ "exit;"
+ :: __imm(bpf_get_prandom_u32)
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: write beyond max outgoing depth")
+__failure
+__msg("stack arg write offset -80 exceeds max 7 stack args")
+__naked void stack_arg_write_beyond_max(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ /* Write to offset -80, way beyond any callee's needs */
+ "*(u64 *)(r11 - 80) = 99;"
+ "*(u64 *)(r11 - 16) = 20;"
+ "*(u64 *)(r11 - 8) = 10;"
+ "call subprog_7args;"
+ "r0 = 0;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: sequential calls reuse slots")
+__failure
+__msg("stack *(R11-8) not properly initialized")
+__naked void stack_arg_sequential_calls(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u64 *)(r11 - 8) = 6;"
+ "*(u64 *)(r11 - 16) = 7;"
+ "call subprog_7args;"
+ "r6 = r0;"
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call subprog_7args;"
+ "r0 += r6;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: r11 load after r11 store")
+__failure
+__msg("r11 load must be before any r11 store or call insn")
+__naked void stack_arg_load_after_store(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u64 *)(r11 - 8) = 6;"
+ "r0 = *(u64 *)(r11 + 8);"
+ "call subprog_6args;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: r11 load after a call")
+__failure
+__msg("r11 load must be before any r11 store or call insn")
+__naked void stack_arg_load_after_call(void)
+{
+ asm volatile (
+ "call %[bpf_get_prandom_u32];"
+ "r0 = *(u64 *)(r11 + 8);"
+ "exit;"
+ :: __imm(bpf_get_prandom_u32)
+ : __clobber_all
+ );
+}
+
+#else
+
+SEC("socket")
+__description("stack_arg is not supported by compiler or jit, use a dummy test")
+__success
+int dummy_test(void)
+{
+ return 0;
+}
+
+#endif
+
+char _license[] SEC("license") = "GPL";
--
2.52.0